1. Field of the Invention
The present invention relates to a method for making a field emission device, and more particularly to a method for making a carbon nanotube-based field emission device.
2. Description of Prior Art
Carbon nanotubes are a novel carbonaceous material discovered by Iijima, a researcher of NEC corporation, in 1991. Relevant information was reported in an article by Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, P56, 1991). Carbon nanotubes can transmit an extreme high electrical current and emit electrons at a very low voltage of less than 100 volts, which make it a very promising potential material for field emission applications.
Referring to FIG. 12, U.S. Pat. No. 6,232,706, invented by Hongjie Dai et al., discloses a field emission device using aligned parallel bundles of carbon nanotubes 200 extending from patterned catalyst layers 230 deposited on a layer of porous silicon 220 which formed on a substrate 210 using a chemical vapor deposition (CVD) process. The carbon nanotubes produced by the CVD process have a variety of heights in a wide range so that the bundles of carbon nanotubes can form a flat top, a bow-shaped top, or other shapes, which are neither predictable nor controllable. Also, a thin layer including disorderly nanotubes, a certain amount of remaining catalyst particles, and amorphous carbon material may be produced on the top of the bundles. All of the above defects may reduce the uniformity and stability of electron emissions from the bundles of carbon nanotubes.